Electron discharge amplifier device employing hollow resonator



A ril 8, 1952 N. c. BARFORD 2,591,910 ELECTRON DISCHARGE AMPLIFIERDEVICE EMPLOYING HOLLOW RESONATOR Filed Oct. 18, 1946 rwswroR NORMHN c.I36 R F RD Patented Apr. 8, 1952 Great Britain Applicationbctolier 18,1946, Serial No. 704.2 In'Great Britain September 10, 1945 e ELECTRONDISCHARGE AMPLIFIER DEVICE EMPLOYINGIIOLLOW RESONATOR Norman CharlesBarford, Southend, England, as-

signor to Electric & Musical Industries Limited, Hayes, Middlesex',England, I a company "of Section 1', Public Law, 690, August 8, 1943 f'Patent expires September 10,1965 iolaims; (c1. 315-'--6) x y r Thisinvention relates to electronfdischarge devices of the kind in whichsignals to jbe amplifiedare fed to a hollow resonator often termed abuncher,- tuned to the frequency of the signals which serves to impartvelocity modulation to a beam of electrons projected through aggapformed therein, the velocity-modulated beam manating from thebuncherbeing thenallow ,to pass through a drift space in which the velocty-modulated beam becomes charge-densitymodulated, after which the beamis caused to pass through a gap in a further resonator, frequentlytermed the catcher, so as to impart energy thereto. Amplifier devices ofthis kind operating, for example, at about 3000 megacycles per secondmay have a bandwidth (between the "half-power points) of about 10megacycles per second. Such a relatively narrow passband may beundesirable in some cases and, accordingly, it is the object of thepresent invention to provide an improved electron ,discharge amplifierdevice employing hollow resonators in which the passband of the deviceas an amplifier is effectively increased.

According to; the invention an electron discharge amplifier device ofthe kind referred to is provided in which one or more further resonatorsis or are arranged between the bunchenand the catcher resonators so 'asto be traverfi i by the electron beam, said one or more furtherresonators being tuned to a frequency or *fr'equencies slightlydifferent from the frequencies to which the buncher and catcherresonators are tuned so as to increase the pass-band of the amplifierdevice.

In order that the said invention may be clearly understood and readilycarried into effect, it will now be more fully described with referenceto the accompanying drawings,inwhich:

Figure 1 is an explanatory curve; Figure 2 illustrates diagrammaticallyan elec tron discharge device constructed according to one embodiment ofthe invention, and

Figures 3 and 4 are further explanatory curves.

The known form of electron discharge'amplifier device hereinbeforereferred to usually has a bandwidth (between the half-power of the orderof 10 megacycles per secoiid at frequencies around 3000 megacycles persecond. In such an amplifier device the output/frequency response curvefor a fixed power source of input would be similar to that indicated inFigure 1 of the drawings. In this case it will be seen that at theresonant frequency in of the resonator maximum output is obtainedwhereas at frequencies removed from the resonant frequency a smalleroutput is obtained. accordance with the present invention one ormorefurther rs'onators is or are arranged between the buncher and catcherresonators so as to be traversed by the electronbeam of thedevice, suchresonator or resonators beingjtuned to a-frequency or frequenciesslightly different from the frequency to which the buncher' and catcherresonatorsare tuned. A typical form of electron'discharge amplifierdevice embodying the invention is shown in Figure 2 of the drawings andcomprises a cathodel, a cathode shield 2, a toroidal first or buncherresonator 3', a toroidal output or catcher resonator 4, and a target 5,theenvelope of the"'-" device being omitted. These two resonatorsfunction in the manner known in the art, input signals applied to thefirst resonator 3-via a coupling loop Sand concentric "line-1causing'the electron stream emanating from the cathode I and passingthrough the resonator 3 to become velocity-modulated and inthedriit'space be tween the resonator 3 and resonator d-the velocity-modulatedstream becomes charge-densitymodulated and on passing through theresonato 4 imparts some of its energy thereto; energy being abstractedfrom this resonator via" coupling loop L, 8 and concentric line 9. Twofurther toroidal resonators In and II are arrangedbetween reso-' nators3 and'4 so as to be traversed'by the elec -f utron' beam, and'theseresonators are tuned, to frequencies f1 and f2, that is to say, tofrequencies on either side of the frequency of in to which theresonators 3 and 4 are tuned. If the resonators 3 and 4 are tuned to3,000 megacycles, the resonators l0 and II may be to 2990 and 3010megacycles respectively. The introduction of the additional resonatorsl0 and II serves to increasethebandwidth of the amplifier device and ifonly one intermediate resonator were employed the bandwidth of theamplifier device would be increased following the curve shown in Figure3, whilst where two intermediate resonators are employed tunedrespectively to frequencies f1 and la the bandwidth of the amplifierdevice would be along the lines of that shown in Figure 4.

It will of course be appreciated that the invention is not limited tothe introduction of one or two intermediate resonators, since more thantwo intermediate resonators can be employed tuned to various frequenciesremoved from the resonant frequency of the buncher and catcherresonators. Further, it is not necessary where two intermediateresonators are employed to have a common wall for the two resonators asindicated in Figure 2.

3 What I claim is: An etres di char e fier d vic comprising cathodemeans for; generating and direct- 4 ing a stream of electrons along abeam path, input resonator means in said path adjacent said cathodemeans and tuned to a first frequency of the order of thousands ofmegacyoles forzvfi i illflv modulating said electrons, output resonatormeans in said path and spaced from saidvelocity modulating means andtuned to said firstfresaid stream, and other means for increasing thebandwidth of said device comprising resonator I io quency for extractingoscillatoryenergy from means in said path intermediate said' velocity,

modulating means and said energy extracting,

means and tuned to a second frequency differing from said firstfrequency by about ten mega cycles.

2. An electron discharge device comprising cathode means for generatingand directing a e m oi l ctrons, al r ibe m pa h, inpu r s-e.

ter: means-in saidpa hadm nt a sa ho means .andtuned; to afirstjrequency for velocity lu g d,. ct n o u onat r means aid p ath andspaced from said velocity quency foriextracting oscillatory energy fromQs eam-La i m ans o in ea h ba d.-

la i am ansa d;fiu edto s ufi t, i

Width 1 sa dfis iq m eo r e na or mea said path -;int erm ediate saidvelocity ana ed aclu in t a i o at r t n to it a sn ies;sli htl eb ye dwc a d-lfi t quenc r pegt l 3. Ameiectron discharge device according toW ereiau a gfi f ue c s r th h s ed q zn acyc e dsa d i 4 An electron.discharge device according to claim- 2, wherein said cavityresonatorshave a mxnpawa h 5. An ielectron discharge amplifier devicecompris ng cathode means ior generating and directing astfeam ofelectrons along a beam path a first icavity resonator, tuned to a firstfrequency so dglsil .m ens and; sa d energy e t t v A.

, e id fier t ere om; by a t e m -Q of the order of thousands ofmegacycles, a second cavity, resonator tuned to a frequency differingfrom said first frequency by about ten ,Inegacycle a third cavityresonator-tuned to said first-frequency, and. a collector electrode,said fourcavity resonators being apertured and arranged along said beampath between said cathode means and said collector electrode in theorder named with said beam path extending through the apertures of theresonators.

7. An electronic amplifier comprising cathode means for producing astream of electrons alon a beam path, velocity modulating resonatormeans in said path adjacent said cathode means andtuned to a firstfrequency, output resonator meansin said path and spaced from saidvelocity modulating resonator means and tuned to said first frequency,other resonator means in said pathintermediate said velocity modulatingresonatormeans and said output resonator means and tunedto a. secondfrequency slightly difierent from saidfirst frequency for increasing thebandwidth of said amplifier, means for coupling said velocity;modulating resonator means to an input signal source, and means forcoupling said output; resonator means to a load, said resonatormeansbeing coupled together only by said stream of electrons.- NORMANCHARLES BARFORD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS j Number 0 Name Date 2,280,824 Hansen et a1. Apr.28, 1942 2,414,843 r Varian et a1 Jan. 28, 1947 2,424,959 Alford Aug. 5,1947 2,452,048 Hansen et a1. Oct.. 26, 1948.

